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Cheops Calibrations
UGE Calibration team : Bruno Chazelas, Mirsad Sarajlic, Michael Sordet, Adrien Deline,
Francois Wildi, Thibault Kuntzer
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Cheops :CHaracterizing ExOPlanet Satellite
● ESA-S , mission● Precsion photometer :
20 ppm photometric precision
● Can be pointed to a large portion of the sky
● Science goal :
– Mass / Radius relation for dense exoplanets (Li Zeng et al, 2017)
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Cheops instrument
● Defocalized telescope● Photometry of a single star● CCD e2v 47-20 : 1024x1024 pixels● Sun-Synchronous ● Field is rotating● Pointing ~ 2-3 arcsec● Data : imagette 200x200
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Calibration Test benchCalibration Source Module :
Super stable sourceNeutral densityFilter wheelMonochromator
CHEOPS TV chamber
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Super Stable source
LDLSLight source
Gamma Scientific photometer
Stability 5 ppm over 24hComputer
Mobile knifeIntegrating sphere
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Calibration Test bench
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Detector chain Calibration
Characteristics Value Comment
RON Nominal 230 kHz
7.2 ADU (14.1 e-)
RON Nominal 100 kHz
3.5 ADU (6.8 e-)
Gain Nominal 230 kHz
0.511 +/- 0.003
Dark 0.056 e-/s
Warm pixels 7 pixelsWith dark above 5 e-/s
Gain temperature sensitivity
-900 ppm/K
Non linearity amplitude
1.2 %
Full well 114-121 ke-
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Flat-fields
● Overall target precision : 0.1 %
● Direct measurement with integrating sphere
– Have to be corrected from sphere non uniformity
– Have to be corrected from distortion
● Spectral reconstruction :
– Monochromator + UVBRI Filter measurement
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Flat-fields : Distortion
● There is more flux on the border of the measured FF
● It does not affect point sources
● If not corrected huge photometric errors
● Recommended to redo measurement in space
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Flat-fields : Distortion measurement
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Flat-field : spectral synthesis
With the calibration measurement one can reproduce with high precision the “real” flat of a source with Smooth spectrum
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Flat-field : spectral synthesis
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Flat-field : precision
● Photometric precision ~ 0.06 %● Error on the correction of the non uniformity of the
integrating sphere ~ 0.04 %● Error due to the distortion correction ~ 0.034 %
● Total error ~ 0.08 %
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PSF
In the center of FoVE90 = 12.8 ± 0.3 pixels
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Performances
● No end-to-end test (lack of time)● But test with integrating sphere
– Temperature stability < 1.5 mK <=> < 2 ppm– Bias voltage stability < 40 µV <=> < 2 ppm – Test bench is the drifting element.– One can give minimum performance achieved
(we are in the right range!)
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Performances
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Conclusion
● All needed calibrations available● Instrument in good shape to make great science● Launch next year